1. Field of the Invention
The present invention relates to a honeycomb structure for use in filters for trapping/collecting particulates in exhaust gas of an internal combustion engine, boiler, and the like, a method for manufacturing the honeycomb structure, and an exhaust gas purification system using the honeycomb structure.
2. Description of the Related Art
Since a large amount of particulates (particulate materials) of which major component is carbon is contained in the exhaust gas exhausted from internal combustion engines such as a diesel engine and such particulates become a cause for the environmental pollution, a filter for trapping/collecting the particulates is sometimes mounted for such internal combustion engines.
In general, as shown in FIG. 6, the filter for use in this purpose includes a plurality of through channels 9 separated by porous partition walls 7 and extending in an axial direction of the honeycomb structure. Predetermined through channels 9a are plugged by plugging portions 11 at one end, and the rest of through channels 9b are plugged at opposite end alternately in the checkered flag pattern in the honeycomb structure for use.
The exhaust gas flows in via one end face 3 of the filter having the honeycomb structure, the particulates included in the gas are removed, and subsequently thus purified gas flows out via the other end face 5. Concretely, the exhaust gas first flows in the through channels 9b whose ends are not plugged at the end face 3 of the filter on an inflow side and whose opposite ends are plugged at the end face 5 on an outflow side, and passes through the porous partition walls 7. The gas moves into the through channels 9a whose ends are plugged at the inlet face 3 and whose opposite ends are not plugged at the outlet face 5, and is exhausted via the through channels 9a. Moreover, at this time, the partition walls 7 acts as filter layers, and the particulates in the gas are trapped by the partition walls 7 and deposited on the partition walls 7.
After the use of this filter for a given period of time, the particulates deposited in the filter are heated by power supplied to an electric heater and burnt/removed. However, they are not completely removed, and some of the particulates remain as ashes (ash content) in the filter. Therefore, in the use over a long period of time, a filter volume substantially decreases, a pressure loss increases, and an amount of particulates which can be trapped/collected decreases, due to the deposited ashes.
Therefore, there is a problem that a frequency at which the particulates are burnt/removed as described above to carry out a regenerative treatment of the filter has to be increased.
To solve this problem, for example, an apparatus has been proposed in which the filter is held so as make the direction thereof vertical to the direction of a gas flow and a vibration apparatus is attached to the filter. The ashes which have fallen from the filter by the vibration applied to the filter by the vibration apparatus are recovered in an ash recovery section disposed below the filter (see JP-A-8-28247).
Moreover, a method has been disclosed in which a high-pressure fluid such as water is jetted onto one end of the filter to clean/remove combustion residual materials adhered onto the filter (see JP-A-2001-50028).
Furthermore, a filter has been disclosed in which one cell wall face is removed from the cell walls in the inlet or outlet face of the filter to form an opening connected to an adjacent cell between the cell walls and the plugging member (see JP-A-60-112618).
Additionally, another filter has been disclosed in which communication holes are made between the cell walls and outer wall (see JP-A-62-75803).
However, these techniques cannot bear practical use, because the opening or the communication hole is not closed with particulates during use and therefore a trapping/collecting efficiency of particulates during use is low. In order to remove the ashes from the filter, a special mechanism or apparatus is required, or the filter needs to be detached from the exhaust system of the filter. Therefore, the techniques have not been very practical.